2 Answers
2

There's a relatively inexpensive procedure, known as the Winkler method, that's used by ecologists to measure the oxygen concentration in streams and ponds. It relies on titration using sodium thiosulfate (among other chemicals).

I don't think this test works on wort, however, due to wort chemistry. At the very least, titration would be difficult with any beer darker than a pale.

The best method is to use a dissolved oxygen (DO) meter. Good DO meters cost around $1000, although I've seen a few handheld units online in the $300 - $500 range.

It's not very common practice to measure wort oxygenation, sadly. Most microbreweries don't even invest in this equipment, although more recently, the trend is changing.

If you have maxed out a lot of other things in your process and really want to make great beer, a DO meter can be a great investment even for home brewing or small craft brewery.
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markusApr 28 at 18:54

I don't know of any homebrewers that are actually measuring the ppm of O2 dissolved in their wort. The best practice is to get an O2 cylinder with a medical grade flow meter (not a pressure regulator, but a flow meter). Then experiment with time on the meter and good results in the final product.